Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

102
FXUS63 KLOT 270752
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
252 AM CDT Sat Jun 27 2026

.KEY MESSAGES...

- Dangerous heat will build across the area next week, with
  afternoon heat index values over 100 degrees each day
  beginning Monday.

&&

.DISCUSSION...
Issued at 252 AM CDT Sat Jun 27 2026

Spotty light showers persist across northern Illinois early
this morning with a lingering low to mid-level deformation axis
wringing out a remaining layer of modest moisture. Expectations
are for remaining showers to erode by mid morning as dry air
advection increases over the area and the deformation axis exits
to the east. For areas south of the Kankakee/Illinois River,
the northern extent of a very moist airmass (PWATS 2+ or higher)
combined with limited low-level capping and diurnal influences
should yield isolated shallow showers with efficient warm rain
processes to develop this afternoon. Expect highs today to range
from the upper 70s inland to the upper 60s along the immediate
shore.

Steepening mid-level lapse rates above an incoming EML on
Sunday will provide at least a small chance for a NW to SE
oriented axis of convection to develop toward the Mississippi
River late tonight. However, limited moisture near the base of
the incoming EML and the lack of a decent LLJ directed toward
the area imply that any upstream convection will struggle to
continue with northeast extent over the area by Sunday morning.
Otherwise, will also need to monitor the track for a potential
MCS developing over South Dakota late this evening as the
notable instability gradient (albeit driven by the incoming EML)
will be focused across northern Illinois Sunday afternoon.

Heat and humidity will begin to build with heat index values
rising into the lower 90s inland during the afternoon, with
persistent onshore flow maintaining much cooler conditions along
the shore.

Focus remains on the potential for an extended period of
dangerous heat through most or all of next week as an
anomalously strong mid-level ridge (heights very near 600dam)
drifting along the Ohio River Valley. H850/H700 temps of over
25C/12C Monday through Wednesday will yield unseasonably warm
conditions with daytime highs well into the 90s while building
an incredibly strong cap over the local area. This should
deflect convection well to the northwest (Minnesota through
Upper Michigan) through at least Wednesday. Combined with
persistent southwest low-level flow, there looks to be no relief
from lake breezes or upstream convective outflow boundaries
during this time. Beyond that point, cooler temps aloft may
allow more robust convective complexes to near from the north
and provide some relief for northern portions of the area. If
this does not occur, similar heat will likely continue heading
into the Independence Day weekend.

For Cook County, current forecast conditions support the
eventual need for an Extreme Heat Watch/Warning for a longer
duration event with afternoon heat index values over 100 degrees
for three days or more in conjunction with nighttime lows
likely struggling to fall much below 80 in the core of the
metro.

For areas outside of Cook County, it appears likely that at
least a Heat Advisory (Heat Index of 105+) will be required for
some days or every day from Monday through Thursday. Whether
conditions meet Extreme Heat Warning criteria (110+) are less
clear and will hinge heavily on whether dew points rise into the
upper 70s versus low to mid 70s.

Kluber

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1233 AM CDT Sat Jun 27 2026

Aviation forecast concerns for the 06Z TAFs:

- Some potential for lowering of VFR ceilings to MVFR Saturday,
  with the greatest likelihood at KGYY. Otherwise, VFR
  conditions expected to prevail.


A west-east oriented, nearly stationary frontal boundary remains
in place to the south of the terminals from central MO into
southern IL/IN early this morning. Aloft, a series of low-
amplitude mid-level disturbances continue to ripple eastward
along the elevated baroclinic zone north of the surface front.
The main effect on weather across the terminals is to maintain
persistent mainly VFR cloud layers in the 4-7 kft range, though
some lower MVFR/IFR bases have been noted along the Lake
Michigan shore and north of KORD where some weak but persistent
sprinkles/drizzle has been occurring since last evening.
Persistent warm/moist advection aloft is produce a gradual
northward shift in the lower VFR deck, resulting in a gradual
lowering of VFR cigs across the terminals. Can`t rule out patchy
MVFR cigs developing as far north as KORD during the day, though
the greatest likelihood of MVFR ceilings appears to be at KGYY
and locations west and south. Lack of any significant
precipitation suggests locations farther north (KRFD/KDPA/KORD
and KMDW) are more likely to remain VFR. High-res guidance
indicates VFR ceilings will persist Saturday night, though may
rise into the ~5 kft range or even scatter out at times.

Surface winds are expected to remain modest (6-11 kts) from the
east-northeast to northeast through the period.

Ratzer

&&

.CLIMATE...
Issued at 252 AM CDT Sat Jun 27 2026

....Daily Records for the Upcoming Week........

Chicago (KORD)
            Record High       Record Warm Minimum
June 29       97 (1954)            80 (1931)
June 30       99 (1953)            80 (2018)
July 1       103 (1956)            78 (1931)
July 2        99 (1970)            79 (1911)
July 3       102 (1949)            78 (1911)
July 4       102 (2012)            80 (1921)


Rockford (KRFD)
            Record High       Record Warm Minimum
June 29      103 (1931)            75 (1931)
June 30      102 (1931)            76 (2018)
July 1       101 (1931)            76 (1970)
July 2        99 (1910)            74 (1970)
July 3        99 (1925)            75 (2012)
July 4       102 (2012)            77 (1977)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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